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BrianBM

Inline engines' pollution characteristics

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A question, that popped into my head for no discernable reason.

 

The most conspicuous inline engine in this country was probably the straight 6 that Jeep dropped some years ago. I comprehend some of the problems of the inline engine (length, for one). Here's a different one ... is an inline engine any more or less difficult, for pollution-control-engineering purposes, then a V-block design? Did that have anything to do with the apparent demise of automotive inline engines in this country?

 

Just curious. Gearheads to the fore!

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I think it does have more to with length issues. With modern designs on newer vehicles with stumpy hoods and smaller engine bays I don't see why emissions would be an engineering problem, as it would be same as an in line 4 just with two more cylinders. How ever VW solved the length issue with the VR6 which posses another question would you consider a VR6 an in line or V-motor? The cylinders are opposed 15 degrees and no valley (single head).

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I share the opinion that the bigger inline engines are gone because of the lack of engine compartment space. However, don't forget that the Cummins diesel in the Dodge 2500/3500 is an inline engine and it does meet the EPA pollution requirements.

 

Getting very specific, I don't think a carburetor-fed, single manifold, inline six cylinder would meet emissions requirements today. Cylinders 1 and 6 suffer from fuel-to-air ratio deficiencies as a result of location. Thus the engine would need a decent amount of exhaust treatment measures.

 

Likewise, an inline six cylinder engine fed with a throttle body plenum and individual cylinder fuel injection would have a similar level of difficulty as many v-block engines when trying to meet emissions standards.

 

Although there is more to this than just emissions. What I notice is the v-block engines that replaced the inline six engines from Ford and Jeep are a smaller displacement. Smaller displacement in both of these cases contributes to less fuel consumption and higher MPG ratings.

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It is packaging, not pollution that has killed most inline 6s. Note that BMW still uses inline 6s, but almost all BMWs are rear wheel drive, with a longitudinal engine.

 

These days, most small and midsize sedans are front-wheel drive, with transverse engines. Six cylinder inline engines are difficult to package this way (though Volvo has done it).

 

For trucks and SUVs, an inline 6 is longer than a V8, requiring a longer hood for crush space.

 

It is too bad, because inline 6s have better vibration characteristics than V6s.

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As said, they do exists in BMW, but with rear wheel drive. I have a VW Jetta Sportwagen and it has a transverse mounted inline 5. So there are other options and combination. VW has some interesting engine, including their W's

 

I'd agree with the others that it is space. I think you can engineer a well designed diesel or gasoline turbo charged 4 and get similar performance as a 6 in a smaller and lighter package. So it may have been a practical decision too.

 

--Pete

 

View PostA question, that popped into my head for no discernable reason.

 

The most conspicuous inline engine in this country was probably the straight 6 that Jeep dropped some years ago. I comprehend some of the problems of the inline engine (length, for one). Here's a different one ... is an inline engine any more or less difficult, for pollution-control-engineering purposes, then a V-block design? Did that have anything to do with the apparent demise of automotive inline engines in this country?

 

Just curious. Gearheads to the fore!

 

 

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Interesting answers; thank you.

 

I assume that the world's remaining I-6 engines are all fuel-injected and 4-valve affairs. Of the remaining I-6 engines, is there one that is, by consensus, the technology leader?

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View PostInteresting answers; thank you.

 

I assume that the world's remaining I-6 engines are all fuel-injected and 4-valve affairs. Of the remaining I-6 engines, is there one that is, by consensus, the technology leader?

 

BMW. You can argue whether it is their twin-turbo inline-6 or their new single turbo inline-6.

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Gm had the 4.2 in the trailblazer and they still have that straight 5 that's in the H3 and little pickups. Volvo has a straight 5 or least they used to. I think the little land rover (lr2) has a straight 6 too. Yeah it's definitely the length that killed it as cars got smaller. I think they might be a little heavier too but not sure.

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